The transcriptional regulation of the genes encoding the two type I collagen chains, alpha1(I) and alpha2(I), is one of special interest because these genes are expressed at widely different levels that correlate with the tissue specificity of collagen synthesis, and with development and maturation of the organism. Furthermore, the genes for alpha1(I) and alpha2(I) are responsive to cues generated by injury and repair, and by a variety of cytokines, hormones, and pharmacological agents. Finally, the expression of type I collagen genes is disturbed in orders such as pulmonary fibrosis and cirrhosis, and in diseases such as scleroderma. Although post-transcriptional mechanisms undoubtedly play an important role in regulating collagen synthesis, there is good evidence that transcriptional control represents the major means by which this regulation is achieved. A major goal of this grant is to determine how this astonishingly intricate pattern of expression is established and maintained,, and how it is altered during development, in response to injury, and in disease. Current studies of gene regulation generally involve the evaluation of mutations in chimeric regulatory/reporter genes in transfection and transgenic experiments. While these approaches represent necessary preliminary steps, it is our contention that definitive results can best be achieved by testing such mutations in the context of the endogenous gene. Gene targeting techniques will therefore be used to create mutations in putative regulatory regions of the Collal gene in mice, and mutant mice will be evaluated for expression of the altered allele and for phenotypic changes. In particular, the proposed experiments will test the hypothesis that modular elements in the Collal gene direct the synthesis of type I collagen selectively to tissues such as skin and bone. It is anticipated that some of the mutations created in mice will generate useful models for human disorders of these tissues, specifically some of the Ehlers-Danlos syndromes and osteoporosis.